为什么复合赋值或迭代运算符不对解除引用的指针起作用

Question

If I want to increment a pointer that's referencing a the location of an int I can't use these methods:

 *Pntr +=1;
 *Pntr++;

However, using this method works with no problems:

 *Pntr = *Pntr + 1;

What's happening that causes these shorthand methods not to work. (Also must point out I'm using Visual Studio and it acts weird at times so I think I should mention that)

Answer 1

*Pntr +=1;

This increments the value the pointer is pointing to.

*Pntr++;

This is the same as:

*(Pntr++);

Which increments the pointer, dereferences the original value of the pointer, and discards the retrieved value.

 *Pntr = *Pntr + 1;

This, like the first line, increments the value the pointer is pointing to.

Answer 2

If I want to increment a pointer that's referencing a the location of an int... [emphasis added]

Note that when you increment a pointer, it gets incremented in steps of the object size that the pointer can point to .

Since you have mentioned -

using this method works with no problems:

*Pntr = *Pntr + 1;

So, it looks like you want to increase the value at location, pointed by Pntr , by 1 .

The precedence of postfix ++ operator is higher than unary * operator (check operator precedence table). So, the expression

*Pntr++;

will be evaluated as

*(Pntr++);

which will move the pointer Pntr by size of int and then dereference it.
To increment the value of pointer, you can do:

(*Pntr)++;

You can also use the prefix ++ operator:

++*Pntr;

The expression

*Pntr +=1;

is same as

*Pntr = *Pntr + 1;

and both will increase the value at location pointed by Pntr by 1 .